Subject: Re: [[IPORPR] cisco srp doubts]

From: Donghui Xie <[email-masked]>
Date: Wed, 30 Jan 2002 13:35:14 -0800

Raj,

Please see inline comments below.

Thanks,
Donghui

>Subject: [IPORPR] cisco srp doubts
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>Hi All,
>
>I'm trying to understand Cisco's SRP implementation and I had a few 
>doubts. I would really appreciate any clarifications.
>
>- A node advertises it's my_usage which has been low pass filtered
>[lp_my_usage - (LP_MU - 1) * lp_my_usage + my_sage / LP_MU].
>Qn : I'm a little confused as to why this is done.

my_usage is a kind of instantaneous bytes count being transmitted which 
usually varies in wide range depending on the ingress traffic burst. 
Running my_usage through a low pass filter (the above formula) yields a 
value without its high frequency noise, that is lp_my_usage. As such, 
lp_my_usage represents a more stable and more accurate measurement of a 
node's bandwidth usage. Advertising lp_my_usage to other nodes helps 
achieving very good stability and convergence of the overall bandwidth 
management in SRP.

>- Topology Discovery related :  ... If there is a wrap on the ring, the 
>wrapped node will indicate a wrap when appending its mac binding and wrap 
>the packet. When the topology packets travel on the wrapped ring, with the 
>ring identifier being different from that of the topology packet itself, ...
>Qn : The ring identifier refers to the R bit in the SRP header would refer 
>to the wrapped ring id (say inner)in question. Right ?
>If so, the macType.RingId in the last mac binding inserted by the wrapped 
>node should be outer, but the Wrapped node is set to 1. Is my 
>understanding correct ?

The R bit and the ring id in topology mac binding should be set to the 
egress ring id of its originator. If the topology discovery packet is 
originated from inner ring, the R bit and the ring id in mac binding should 
be 1. When the topology discovery packet is received by a wrapped node on 
the inner ring, this node would append its mac binding with its ring id 1 
and wrapped node bit 1, the packet would be then actually transmitted to 
outer ring by the node.

>Qn : The way a node figures out if a particular topology message is a 
>wrapped message is by inspecting the macType.wrappednode of the last mac 
>binding. Is this correct ?

No. It inspects whether the ring id bit in the last mac binding matches the 
rind id on which the topology discovery packet is being received.

>Thanks,
>
>-- Raj
>
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